This invention relates to the field of adaptive optics systems and more particularly to real time optical wavefront sensors utilizing two beam phase modulating digital interferometers to characterize optical wavefront distortions.
Real time optical wavefront sensors are used to measure unwanted propagation path aberrations, such as atmospheric turbulence that distorts optical signals and degrades performance of optical processing systems. Characterizing the unwanted aberration permits correction for the aberration and the generation of an undistorted wavefront. Applications include direct line of sight communication systems and ground based telescopes limited by resolving power due to atmospheric distortions.
In addition, real time optical wavefront sensors are employed to determine the profile of an optical wavefront to allow for characterization of the medium of optical signal travel. Here, characterization of the wavefront profile is the information of interest. Applications include the analysis of phase objects such as optical components, biological samples, and the atmosphere.
A wavefront sensing technique that characterizes the phase profile of an optical path is disclosed by John W. Hardy; "Active Optics: A New Technology for Control of Light" Proceedings of the IEEE, Vol. 66, No. 6, June 1978. In this type of system, the real-time direct wavefront measuring system employs detectors to measure the relative phase shift of two beams. Appropriate instrumentation is utilized to construct the phase profile from the phase detector measurement. A primary shortcoming of a system described above is the greatly limited spatial bandwidth due to the requirement of having a phase measuring channel for each measurement location. Furthermore, typical of the prior art, these systems and systems known to those versed in the art which implement similar techniques, tend to have large computational requirements and subsequently operate at extremely slow system speeds.
Another type of wavefront sensing technique is the method described by Glen W. Johnson et al; Optics Engineering, Vol. 18, No. 1, January-February, 1979. This type of wavefront measuring system employs sinusoidal modulation of the reference wavefront and appropriate instrumentation to measure the local slope differential at a given location in the sensor's aperture between a phase modulated reference wave and an interference wave. A primary shortcoming in utilizing a technique as described is the computational requirements in generating the phase profile from the acquisition data to realize a real-time wavefront characterizing system.
It is an object of this invention to provide an improved optical wavefront measuring system.
Another object is to provide an improved system for characterizing the propagation path for an optical signal.
Yet another object is to provide a direct wavefront measuring system that utilizes the intensity information of the interference wave generated from a temporally phase modulated reference wave and a wave modified by an optical path to be measured to construct the phase profile of the optical path.